Pakistan launched its first major operation against the militant group accused of carrying out the Mumbai attacks, raiding a camp of Lashkar-e-Taiba and capturing a man identified by India as one of the masterminds behind the terrorist strike.

According to local reports, 12 members of the banned group including Zaki-ur-Rehman Lakhvi, accused by Delhi as being one of the planners of the carnage in India's financial centre, were arrested in Sunday night's raid in the hills above Muzaffarabad, the capital of Pakistan-controlled Kashmir. A helicopter gunship hovered overhead and gunfire was heard.

Some Indian officials privately described it as "an important first step", though there was some scepticism in India about the nature of the raid. The "camp" that was stormed included a hospital, a madrasa (Islamic school) and offices. However, it was unclear whether it was a training facility for militants or just an administrative and charitable site.

The complex was ostensibly being used by Jama't-ud-Da'wah, an Islamic organisation that it believed to be a front for the banned Lashkar-e-Taiba (LeT) but claims no links. The camp was subsequently cordoned off.

The Pakistan army acknowledged the raid but provided few details.

"This is an intelligence-led operation against banned militant outfits," said Major General Athar Abbas, the chief spokesman of the Pakistani army. "There have been arrests and investigations are on. We are not disclosing any names ... Further details will be available after preliminary investigations."

There was no move against LeT's alleged headquarters in Muridke, an hour's drive from Lahore. The group has denied involvement in the Mumbai attacks.

Muzaffarabad is the nerve-centre of jihadi activity aimed across the line of control at the portion of Kashmir ruled by India. The three-day Mumbai siege of started on November 26 and left almost 200 people dead.

Lakhvi was supposed to be LeT's operations chief and, according to some reports, recruited Ajmal Ameer Kasab, the lone gunman caught alive during the Mumbai assault. There was no word on what happened to Lakhvi after the arrest or on the whereabouts of Yusuf Muzammil, who has been named by Delhi as the other main planner of the Mumbai attack.

It has been reported that the Indian authorities have asked for the two men to be handed over. Some locals in Muzaffarabad suggested the raid may have been staged in some aspects, with rumours that the militants were tipped off beforehand.

In the past, Pakistan has arrested the founder of LeT, Hafiz Saeed, but then quietly let him go weeks later.

Analysts see little chance that Lakhvi or any other major LeT commander will be handed over to India. The Pakistani president, Ali Asif Zardari, has said that anyone detained in Pakistan will be tried there.

Islamabad is under intense international pressure to act against LeT, which was officially banned in 2002. But any concerted attempt by the Pakistani authorities to suppress the militant group further would be likely be met with a violent response by the group and a political backlash in Pakistan, placing Islamabad in a no-win position.

The government yesterday again complained that India had not shared evidence it had claimed it had on the participation of groups or individuals based in Pakistan. Islamabad also proposed that it would send a "high-level delegation" to Delhi.

"The main site of LeT is Muridke, Lahore, but they haven't done that," said Vikram Sood, an analyst in Delhi and former head of India's Research and Analysis Wing intelligence agency. "I wouldn't say this is a major move but I think it's to pre-empt any [Indian] action."

Within Pakistan, the religious right was scathing over the Muzaffarabad raid.

"We've known for a long time that [the camp] was there. If we wanted to take action, we should have done so, but not under the external pressure we now face," said Fazlur Rehman, head of the Jamiat Ulema-e-Islam, a hardline religious party, part of the ruling coalition in Islamabad.

Qazi Hussain Ahmad, head of Pakistan's other main religious party, Jamaat-e-Islami, said: "This [raid] is wrong. It's all a conspiracy by India and the US. This action shows up the weakness of this [Pakistani] government."